1. Field of Invention
The present invention relates to the field of agriculture and more specifically to the field of combatting plant diseases and injuries by a pathogen by means of a composition comprising a natural polysaccharide, chitosan, as a main ingredient, an organic acid, and, as desired, various biologically active substances for enhancing their effect.
The present invention is much superior to any agricultural chemicals (pesticides) currently used in terms of environmental safety, can be used widely as a biological agent against diseases of, and injuries to, crops and has equal or better effects on pathogens compared to the above pesticides, for the treatment of seeds and saplings before seeding of crops, for treatment of plants during growth, and for application to the soil before dissemination (planting).
2. Related Art
Compositions comprising chitosan as a main ingredient for use in cultivation of agricultural plants as the plant growth regulator have already been known (U.S. Pat. No. 4,312,159). The known compositions include the following compounds (% by volume):
wherein the weight ratio of chitosan to glutamic acid is 1:1.
Major disadvantages of the known compositions comprising chitosan as a main ingredient include its narrow range of functions, i.e., they function only as the plant growth regulators.
By analyzing the conventional state of the art, it was found that the activity so far known for chitosan and organic acids as well as all biologically active substances (excluding catapol, salicylic acid, and monosubstituted orthophosphite sodium) is only the growth regulating action. For catapol, only the fungicidal and the algicidal actions are so far known. Salicylic acid has been used as a fungicide and for treatment of rheumatoid diseases. For monosubstituted orthophosphite sodium, the prevention of mycosis of the seeds of the grass plants and other garden plants has been known.
Thus, the purpose of the present invention is to provide a novel composition which is capable of imparting to plants not only the ability of controlling the growth of the plants but resistance to a wide range of plant pathogens.
According to the first embodiment of the invention, the present invention provides a composition for enhancing resistance to plant diseases comprising the following ingredients:
(1) chitosan with a molecular weight of 800-150,000 and a degree of deacetylation of 65-97% 0.004-0.500% by weight;
(2) the following organic acids or a mixture of the organic acids (a) and (b) 0.004-0.500% by weight
(a) lactic acid or succinic acid or both;
(b) lactic acid or succinic acid or both, and glutamic acid or a salt thereof;
(3) one to three biologically active substances selected from the group consisting of a natural or synthetic plant hormone, a natural unsaturated fatty acid or a synthetic derivative thereof, an alkyldimethylbenzyl ammonium salt of a copolymer of N-vinyl pyrrolidone and crotonic acid, phenolic acid, and an inorganic salt; and
(4) water all of the remainder,
wherein the weight ratio of the ingredient (1) and the ingredient (2) is 1:1, the weight ratio of the ingredient (3) and the ingredient (1) is 0.0002-2:1, and pH is 5.6-6.0.
As the plant hormone in the above ingredient (3), there can be mentioned heteroauxin (xcex2-indol acetate, IAA), a synthetic fluorine compound such as FF806, and the like. As the natural unsaturated fatty acid or a synthetic derivative thereof in said ingredient (3) there can be mentioned oleic acid, linoleic acid, linolenic acid, arachidonic acid or 12-oxy-cis-9-octadecenic acid methyl ether, and the like. Furthermore, as the phenolic acid in said ingredient (3), there can be mentioned, for example, salicylic acid. As the inorganic acid salt ins said ingredient (3), there can be mentioned monosodium phosphite.
According to the second embodiment of the present invention, there is provided a composition for enhancing resistance to plant diseases comprising the following ingredients:
(1) chitosan with a molecular weight of 41,600-800,000 and a degree of deacetylation of 75-90% 0.004-0.500% by weight;
(2) the following organic acids or a mixture of the organic acids (a) and (b) 0.004-0.500% by weight
(a) lactic acid or succinic acid or both of the two;
(b) lactic acid or succinic acid or both of the two and glutamic acid or a salt thereof;
(3) water all of the remainder,
wherein the weight ratio of the ingredient (1) and the ingredient (2) is 1:1.
Preferably, the above essential ingredients are supplemented, as an optional component, with a biologically active substance (3) which is a natural or synthetic plant hormone, a natural unsaturated fatty acid or a synthetic derivative thereof as the optional ingredients. As said natural or synthetic plant hormone as the above optional ingredient, for example, there can be mentioned heteroauxin, fluoroxane(xcex1-(4-methylaminobenzene)-xcex2, xcex2, xcex2-trifluorolactic acid ethylether hydrochloride), a synthetic fluorine compound such as FF-806, and the like. Furthermore, as said natural unsaturated fatty acid or a synthetic derivative thereof as the above optional ingredient, there can be mentioned, for example, arachidonic acid, a methyl ether of 12-oxy-cis-9-octadecenic acid, and the like.
Chitosan is a natural polysaccharide, xcex2-(1-4)-2-acetamide-2-deoxy-D-glucopyranoside, having a polymeric ring structure, and is represented by the following structural formula: 
wherein, m+n is 100 mole %, n is 65-97 mole %, and the molecular weight is 300-1,000,000. In the first embodiment of the present invention, preferably the chitosan has n (degree of deacetylation) of 65-97%, and a molecular weight of 800-150,000. In the second embodiment of the present invention, the chitosan has n (degree of deacetylation) of 75-90%, and a molecular weight of 41,600-800,000.
Heteroauxin (xcex2-indol acetate, IAA), a natural plant hormone, is a hormone having the growth promoting activity and is represented by the following chemical formula: 
Fluoroxane, a synthetic derivative of a plant hormone, is xcex1-(4-methylamino benzene)-xcex2, xcex2, xcex2 trifluorolactic acid ethyl ether hydrochloride which has the ability of controling growth (control of cell division) and is represented by the following formula: 
FF-806 is a synthetic fluorine compound having the ability of controling plant growth and is represented by the following formula: 
An alkyl dimethyl benzyl ammonium salt of a copolymer of N-vinyl pyrrolidone and crotonic acid is also called catapol and is represented by the following formula: 
wherein, m=80-85 mole %, k=15-20 mole % R=CnH2nxe2x88x921, n=10-18, and the molecular weight is 12,000-400,000 D.
The methyl ether of 12-oxy-cis-9-octadecenic acid has the ability of controling plant growth and is represented by the following formula:
CH3xe2x80x94(CH2)4xe2x80x94(CHxe2x95x90CHxe2x80x94CH2)4xe2x80x94CH2CH2xe2x80x94COOCH3.
The composition of the present invention may be obtained by dissolving chitosan in an aqueous solution of lactic acid, succinic acid, or a mixture thereof and glutamic acid with the weight ratio of chitosan and the organic acids being 1:1. The other biologically active substance additives are added to this solution as an aqueous solution. When desired (for example, in the case of IAA and FF-806), a small amount of dimethyl sulfoxide (0.05-0.1% of the final concentration of the composition) is used.
The possibility of using the composition of the present invention discovered by the inventors as an environmentally-safe biologically-active agent for plants is not obviously derived from the structure and the known property of each ingredient and the overall composition.
The effect of these compositions are inferably derived from the previously unknown ability of chitosan to enhance a nonspecific plant""s resistance to harmful organisms in general as an environmentally-safe biologically-active agent. This is endorsed by Table 1. The composition of the present invention is soluble in water, has a favorable coat-forming property and permeability, has a high attachment property to the plants, is active and stable at around a neutral pH of 5.6-6.0 (when desired, pH may be adjusted by adding sodium carbonate), and has no plant toxins.
In order to demonstrate that the proposed solution is consistent with the conditions for xe2x80x9cindustrial applicabilityxe2x80x9d and to permit better understanding of the nature of the invention, specific examples are presented below. However, it should be noted that the nature of the present invention is not limited to these examples.
The activity of the composition of the present invention as an environmentally-safe plant protecting agent active against a wide range of pathogens at various stages of plant growth was discovered for the first time by the inventor of the present invention, and the activity cannot be obviously derived from the structures and the known properties of these compositions and the ingredients thereof as a whole.
As far as can be inferred, the effect of the composition of the present invention is based on the so far unknown ability of chitosan that, when the environmentally-safe biologically active chitosan is combined with other ingredients of the composition, acts as a plant activating agent which is resistant to diseases caused by a series of harmful organisms, due to differences in the material metabolism between the pathogen and the plant.
The substances having the above-mentioned activity are limited to particular combinations of chitosan with strictly specified organic acids and several other compounds. This is related to the fact that the present composition induces disease resistance in plants by the following two methods:
By the increase in the oxidation potential of the cell. The oxidation potential is enhanced by the natural fatty acids having unsaturated (double) bonds (oleic acid, linoleic acid, linolenic acid, and arachidonic acid) or the unsaturated analogues thereof (local disease-resistance).
By the activation of the protective genes of plants. This activation is derived from the presence of a specific natural or synthetic hormone (for example, IAA, and FF-806), a phenolic acid (for example, salicylic acid) and an inorganic acid (for example, NaH2PO4) in the ingredients of the composition, which causes systemic disease resistance in the plant tissues.
Therefore, by various biologically active substances and the compositions thereof, the same technical results (the enhancement of disease resistance in plants) can be obtained by the same method.
The composition of the present invention is soluble in water, has a favorable coat-forming property and permeability, has a high adherent property to the plants, is active and stable at around a neutral pH of 5.6-6.0 (when desired, pH may be adjusted by adding sodium carbonate), and has no toxicity to plants in the range of concentrations commonly used.
By utilizing the present invention, even a marked reduction in the concentration of a biologically active substance (heteroauxin 2 g, fluoroxane 0.2 g, FF-800 5 g, catapol 25-1.0 kg) can provide remarkably good protective results against diseases and injuries to crops, which leads to the improvement of ecologically-acceptable labor conditions and the prevention of contamination of the environment and crops by residual agricultural chemicals.